1900

• Marie Curie discovers that an atom can spontaneously break apart, releasing energy. Scientists call this phenomenon "radioactivity."
• Sigmund Freud publishes On the Interpretation of Dreams in German.
• In April, Thomas Alva Edison invents the nickel-alkaline storage battery.
• On May 14, Dutch botanist Hugo de Vries announces his discovery of Austrian monk Gregor Mendel's three laws of genetics. Later in 1900, two other scientists, Carl Correns and Erich Tschermak, claim the same discovery.
• In July, geologists at the University of Berlin in Germany invent the modern pendulum seismograph for the detection of earthquakes. U.S. universities, led by the University of California, Berkeley, build seismographs in their geology departments.
• On July 2, the first zeppelin dirigible flies in Germany.
• In October, the U.S. Army builds its first dirigible. The army will use...